Topband: K9AY-Loop ?

[n4is]

Jerry

>Topbanders,
>i recently built a K9AY-Loop ( switchable N/S E/W on a single Mast), but
>i am not satisfied with it's performance.
>

I'm quite sure there is no problem with your K9AY-Loop itself; however I am
100% sure why it is not working.

The main reason RX antennas do not work is because the proximity with a
resonant TX antenna. 

It is very well understood how a Yagi antenna works when it is transmitting,
the reflector and the director reradiate the energy from the driver element
and due the phase the final field diagram has directivity and gain. 

The same happens during RX, the reradiated signal from the director and
reflector adds to driver signal and the receiver gain is the same as TX
gain.

When you have a TX antenna close to resonance 1/2 wave, or 1/4 vertical TX
antenna, the same reradiation occurs. 

In my system, I detune my TX antenna and the impact on the noise on my RX
antenna is -6 to -20 db depending on the direction of my WF is receiving.
Without detuning my TX antenna my WF does not work at all. You can see both
charts on my web site.

http://www.n4is.com/waller/BIG_DUAL_LOOP.html

Check; Waller Flag polar plot without detuning.

Another very important point, I can say it is a "must have thing", is choke
the RX feed line. Common mode noise can destroy any directivity receiving
signal from the shield of the RX feed line. Of course; a very good ground is
necessary to make the choke work.

My WF has several chokes, however the one at the end of the vertical droop
of RX feed line is critical, I can recommend > 3K or 40 db attenuation at
that point. Without this choke the feed line become a vertical antenna
inside the flags. The issue here is that you can not measure the noise
impact that choke makes, I removed it for a test the impact was at 6 to 10
db in my noise floor.

N8PR just got his WF working right, the big problem Pete antenna was not
working first place was that choke, after Pete install a choke with 6inch
and 50 turns of RG58 at both sides of the ground rod, his WF starts to work
as a champ.

I hope this help you and many others hams with bad experience using Flags,
EWE or small receiver antennas.

Regards
Carlos
N4IS










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